This invention relates to a linear tape storage system represented by DLT (digital liner tape) or LTO (linear tape open) and, in particular, to a magnetic tape head actuator assembly (or a head sending mechanism) and a backlash eliminating mechanism (or a wobble prevention mechanism) thereof.
Linear tape storage systems (magnetic recording/reproducing apparatus) of the type described are developed as xe2x80x9cbackupxe2x80x9d systems for memory devices (e.g. hard disks) of computer systems and various types of the linear tape storage systems have been proposed in prior art. For example, a digital linear tape drive serving as the DLT is disclosed in U.S. Pat. No. 5,862,014 to Nute, entitled: xe2x80x9cMulti-Channel Magnetic Tape Head Module Including Flex Circuitxe2x80x9d or the like.
The digital linear tape drive (which may be merely called xe2x80x9cdriving apparatusxe2x80x9d, xe2x80x9ctape drivexe2x80x9d, or xe2x80x9cdrivexe2x80x9d) is for receiving a tape cartridge (which may be merely called xe2x80x9ccartridgexe2x80x9d) having a single reel (a supply reel) and contains a take-up reel therein. When the tape cartridge is installed in the driving apparatus, a magnetic tape is pulled out of the tape cartridge and then is wound by the take-up reel through a head guide assembly (HGA). The head guide assembly is for guiding the magnetic tape (which may be merely called xe2x80x9ctapexe2x80x9d) pulled out of the tape cartridge to a magnetic head. The magnetic head exchanges information between the tape and the magnetic head. The head guide assembly generally comprises a boomerang-shaped aluminum plate and six large guide rollers each using a bearing.
In addition, the head guide assembly is also called a tape guide assembly which is disclosed, for example, in U.S. Pat. No. 5,414,585 to Saliba, entitled: xe2x80x9cRotating Tape Edge Guidexe2x80x9d. Furthermore, an example of the guide roller is disclosed in Japanese Unexamined Patent Publication No. 2000-100025 (JP 2000-100025 A).
The tape drive is generally comprised of a rectangular housing that has a common base as described, for example, in U.S. Pat. No. 5,793,574, entitled: xe2x80x9cTape Head Actuator Assembly Having A Shock Suppression Sleevexe2x80x9d to Cranson et al. The base has two spindle motors (reel motors). The first spindle motor has a spool (or a take-up reel) permanently mounted on the base and the spool is dimensioned to accept a relatively high speed streaming magnetic tape. The second spindle motor (reel motor) is adapted to accept a removable tape cartridge. The removable tape cartridge is manually or automatically inserted into the drive via a slot formed on the drive""s housing. Upon insertion of the tape cartridge into the slot, the cartridge engages with the second spindle motor (reel motor). Prior to rotation of the first and the second spindle motors, the tape cartridge is connected to the permanently mounted spool (the take-up reel) by means of a mechanical buckling mechanism. A number of rollers (guide rollers) positioned, as intermediates, between the tape cartridge and the permanent spool guide the magnetic tape as it traverses at relatively high speeds back and forth between the tape cartridge and the permanently mounted spool.
In the digital linear tape drive having such a structure, an apparatus for pulling the tape from the supply reel to the take-up reel is required. Such as a pulling apparatus is disclosed, for example, in International Publication No. WO 86/07471. According to WO 86/07471, take up leader means (a first tape leader) is coupled to the take-up reel while supply tape leader means (a second tape leader) is connected to the tape on the supply reel. The first tape leader has one end formed into a mushroom like tab. The second tape leader has a locking aperture. The tab is engaged into the locking aperture.
Furthermore, a mechanism for joining the first tape leader with the second tape leader is required. Such a joining mechanism is disclosed, for example, in International Publication No. WO 86/07295.
In addition, Japanese Unexamined Patent Publication No. 2000-100116 (JP 2000-100116 A) discloses a structure of leader tape engaging part which can engage an end part of a leader tape (the second tape leader) to a tape end hooking part in a tape cartridge without requiring a tab projected in the side of the leader tape.
U.S. Pat. No. 5,857,634, entitled: xe2x80x9cTake-up Reel Lockxe2x80x9d to Hertrich discloses a locking system for preventing a take-up reel of a tape drive from rotating when a tape cartridge is not inserted to the drive.
On the other hand, an example of the tape cartridge installed in the digital linear tape drive is disclosed in Japanese Unexamined Patent Publication No. 2000-149491 (JP 2000-149491 A).
In addition, U.S. Pat. No. 6,241,171, entitled: xe2x80x9cLeaderless Tape Drivexe2x80x9d to Gaboury discloses a tape drive wherein a tape leader from a tape cartridge is urged through a tape path, into a take-up reel, and secured therein without the use of a buckling mechanism or a take-up leader.
In addition, the tape drive further comprises a magnetic tape head actuator assembly which is located between a take-up spool and a tape cartridge on a tape path defined by a plurality of rollers. During operation, a magnetic tape flows forward and backward between the take-up spool and the tape cartridge and is closely adjacent to the tape head actuator assembly while the magnetic tape flows on the defined tape path. An example of such as a magnetic tape head actuator assembly is disclosed in the above-mentioned U.S. Pat. No. 5,793,574.
The magnetic tape head actuator assembly comprises a tape head assembly and a head sending mechanism. The tape head assembly comprises a magnetic head and a head holder for holding the magnetic head. On the other hand, the head sending mechanism comprises a lead screw having a rotation axis and an external thread, a split nut having an internal thread engaging with the external thread of the lead screw, and a head lift for engaging the split nut and for holding the tape head assembly.
The magnetic tape head actuator assembly is mounted on a chassis of the tape drive. In this situation, rotation of the lead screw moves both of the split nut and the head lift up and down along the rotation axis of the lead screw and thereby moves the head assembly up and down.
To eliminate backlash between the lead screw and the split nut, an annular channel is formed at a peripheral surface of the split nut and a doughnut spring is located in the annular channel. The doughnut spring is a special coil spring formed into a doughnut shape. The doughnut spring elastically changes the shape of the split nut so as to press the split nut from the outside into the inside against the lead screw.
As mentioned above, the combination of the split nut and the doughnut spring is used as a backlash eliminating mechanism (or a wobble prevention mechanism) in the conventional magnetic tape head actuator assembly. However, the split nut and the doughnut spring are expensive because of their special shapes (or structures). Furthermore, the split nut has elasticity with a manufacturing variation and the same is true for the doughnut spring. Accordingly, it is difficult to obtain fixed pressing power from the split nut against the lead screw.
In addition, the conventional head sending mechanism comprises a bearing for the lead screw and a guide for preventing the head lift from rotating which are apart from the split nut. Thus, the head sending mechanism is expensive and it is difficult to mount the head sending mechanism on the chassis of the tape drive.
It is therefore an object of this invention to provide a head sending mechanism (or an actuator assembly) with a backlash eliminating mechanism which can substantially eliminate backlash of the head sending mechanism by means of inexpensive structure (or by using inexpensive parts).
It is another object of this invention to provide a head sending mechanism (or an actuator assembly) with a backlash eliminating mechanism which can obtain fixed pressing power.
It is still another object of this invention to provide a head sending mechanism (or an actuator assembly) which is inexpensive.
It is yet still another object of this invention to provide a head sending mechanism (or an actuator assembly) capable of reducing the number of assembling processes.
Other object of this invention will become clear as the description proceeds.
According to the aspect of this invention, a head sending mechanism is for sending a head assembly up and down along a predetermined axis extending in an up and down direction. The head sending mechanism comprises a lead screw with an external thread having a rotation axis corresponding to the predetermined axis. A head lift on which the head assembly is mounted provides a through hole from a lower side to an upper side thereof in the up and down direction and freely receives the lead screw. The head lift further provides a middle space which is open to the outside of the head lift and partly coincides with the through hole at the middle thereof in the up and down direction. A head guide is fixed at the lower side of the head lift and has a first internal thread for engaging with the external thread of the lead screw. The head guide moves the head lift up and down along the predetermined axis according to rotation of the lead screw around the rotation axis. A preload bushing is located in the middle space of the head lift so as to be out of contact with the head lift in the up and down direction and not to rotate around the rotation axis. The preload bushing has a second internal thread for engaging with the external thread of the lead screw. A compressed coil spring is located between the head lift and the preload bushing in the middle space of the head lift and presses the head lift against the preload bushing along the predetermined axis.
According to another aspect of this invention, a backlash eliminating mechanism is for use in a head sending mechanism for sending a head assembly up and down along a predetermined axis extending in an up and down direction. The head sending mechanism comprises a lead screw with an external thread having a rotation axis corresponding to the predetermined axis. A head lift on which the head assembly is mounted provides a through hole from a lower side to an upper side thereof in the up and down direction and freely receives the lead screw. An up-down moving member is fixed at the lower side of the head lift and has a first internal thread for engaging with the external thread of the lead screw. The up-down moving member moves the head lift up and down along the predetermined axis according to rotation of the lead screw around the rotation axis. The backlash eliminating mechanism comprises a pressing means which is related to both of the lead screw and the head lift and always presses the head lift in a direction along the predetermined axis.
In the backlash eliminating mechanism, the head lift further provides a middle space which is open to the outside of the head lift and partly coincides with the through hole at the middle thereof in the up and down direction. The pressing means comprises a preload bushing located in the middle space of the head lift so as to be out of contact with the head lift in the up and down direction and not to rotate around said rotation axis. The preload bushing has a second internal thread for engaging with the external thread of the lead screw. A compressed coil spring is located between the head lift and the preload bushing in the middle space of the head lift and presses the head lift against the preload bushing along the predetermined axis.
According to still another aspect of this invention, an actuator assembly is for moving a mounted body along a predetermined axis in an up and down direction by rotating a lead screw with an external thread. The lead screw has a rotating axis corresponding to the predetermined axis. The actuator assembly comprises a mounting member on which the mounted body is mounted. The mounting member provides a through hole from a lower side and an upper side thereof in the up and down direction and freely receives the lead screw. A moving member is fixed at the lower side of the mounting member and has a first internal thread for engaging with the external thread of the lead screw to move the mounting member up and down along the predetermined axis according to rotation of the lead screw around the rotation axis. A backlash eliminating mechanism is related to both of the lead screw and the mounting member and always presses the mounting member in a direction along the predetermined axis.
In the actuator assembly, the mounting member further provides an middle space which is open to the outside of the mounting member and partly coincides with the through hole at the middle thereof in the up and down direction. The backlash eliminating mechanism comprises a preload bushing located in the middle space of the mounting member so as to be out of contact with the mounting member in the up and down direction and not to rotate around the rotation axis. The preload bushing has a second internal thread for engaging with the external thread of the lead screw. A compressed coil spring is located between the head lift and the preload bushing in the middle space of the mounting member and presses the mounting member against the preload bushing along the predetermined axis.